Transparent conductive laminate film, touch panel having this transparent conductive laminate film, and production method for this transparent conductive laminate film

ABSTRACT

A touch panel-use transparent conductive laminate film little in coloring of transmitted beam and high in transmittance. The transparent conductive laminate film ( 100 ) comprises an intermediate layer (B) laminated on a transparent substrate(A) and having an optical film thickness of 100-175 nm, and a conductive layer (C) having an optical film thickness of 10-60 nm, the refractive index of the intermediate layer being between that of the substrate and that of the conductive layer at 1.7-1.85.

TECHNICAL FIELD

The present invention relates to a transparent conductive laminate filmwhich is simple, low in production cost and little in coloring, and atouch panel using the same.

BACKGROUND ART

A touch panel is known as a device provided on a display surface ofvarious display apparatuses, such as a liquid crystal display and acathode ray tube (CRT), and enables input of information by touching thescreen. Typical forms of touch panels include a resistive touch panelhaving two electrode substrates which are arranged so that theconductive layer provided on each substrate is faced with each other.

Conventional electrode substrates for resistive touch panels include asubstrate made of a glass plate, a resin plate or a thermoplasticpolymer film, and a conductive layer formed on the substrate. Theconductive layer contains a conductive metal oxide such as indium tinoxide (ITO) and zinc oxide.

In conventional electrode substrates, transmittance of visible lighthaving a relatively short wavelength is decreased due to reflection andabsorption on the conductive layer. The total transmittance is thereforedecreased and the light transmitted through the touch panel becomesyellow or brown, making it difficult to show accurate color of thedisplay device on the touch panel.

In order to solve the problem, Japanese Patent Laid-Open Publication No.6-218864 as the first prior art proposes a laminate in which a highrefractive index layer having a refractive index higher than that ofboth the conductive layer and the substrate is formed between theconductive layer and the substrate, and a laminate in which a lowrefractive index layer having a refractive index lower than that of boththe conductive layer and the substrate is formed between the conductivelayer and the substrate. According to the first prior art laminates, thereflectance at a wavelength around 550 nm is decreased as shown in FIG.5, while the transmittance at a wavelength around 550 nm is improved asshown in FIG. 6. Consequently, the total transmittance is improved.However, the problem of coloring of transmitted light to yellow or brownhas not been solved.

Japanese Patent Laid-Open Publication No. 11-286066 as the second priorart proposes a conductive film in which a multilayer optical film islaminated between the conductive layer and the substrate.

The second prior art conductive film, however, has complicated structureand is high in production cost because it has a number of optical films.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a transparentconductive laminate film which is simple, low in production cost andlittle in coloring of transmitted light, and a touch panel provided withthe laminate film.

The present inventors have found that a transparent conductive materialcapable of preventing coloring of transmitted light can be produced bylaminating a substrate, an intermediate refractive index layer havingspecific properties and a conductive layer having specific properties ina specific order.

According to an aspect of the present invention, a transparentconductive laminate film including a light transmitting substrate, anintermediate layer laminated on one or both surfaces of the substratedirectly or indirectly via at least one layer and a conductive layerlaminated on the intermediate layer is provided. The optical thicknessof the intermediate layer is 100 to 175 nm and the optical thickness ofthe conductive layer is 10 to 60 nm. The intermediate layer has arefractive index of 1.7 to 1.85, which is between that of the substrateand that of the conductive layer.

According to another aspect of the present invention, a method ofproducing a transparent conductive laminate film is provided. The methodincludes providing a light transmitting substrate, forming on onesurface of the substrate an intermediate layer having an opticalthickness of 100 to 175 nm and a refractive index of 1.7 to 1.85 whichis greater than the refractive index of a substrate and forming on theintermediate layer a conductive layer having an optical thickness of 10to 60 nm and a refractive index greater than the refractive index of theintermediate layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of a transparent conductivelaminate film of Example 1 of the present invention;

FIG. 2 is a schematic cross sectional view of a touch panel of Example 5of the present invention;

FIG. 3 and FIG. 4 are graphs showing reflectance and transmittance ofthe transparent conductive laminate film of a preferred embodiment ofthe present invention, respectively; and

FIG. 5 and FIG. 6 are graphs showing reflectance and transmittance of aconventional transparent conductive laminate film, respectively.

“DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT”

A preferred embodiment of the present invention will now be described indetail.

A transparent conductive laminate film according to a preferredembodiment includes a light transmitting substrate A, an intermediaterefractive index layer B laminated on one or both surfaces of thesubstrate A directly or indirectly via at least one layer and aconductive layer C. The optical thickness of the intermediate refractiveindex layer B is 100 to 175 nm and the optical thickness of theconductive layer C is 10 to 60 nm. The refractive index of theintermediate refractive index layer B is 1.7 to 1.85, and the refractiveindex of the substrate A is less than the refractive index of theintermediate refractive index layer B, and the refractive index of theintermediate refractive index layer B is less than the refractive indexof the conductive layer C (refractive index of substrate A<refractiveindex of intermediate refractive index layer B<refractive index ofconductive layer C). The optical thickness refers to the product (n×d)of refractive index n and thickness d of a layer.

The substrate A is not particularly limited as long as it is a knowntransparent material. As the substrate A, for example, glass ortransparent resins such as polyethylene terephthalate (PET),polybutylene terephthalate, polycarbonate, a poly(methyl methacrylate)copolymer, triacetyl cellulose, polyolefin, polyamide, poly(vinylchloride) and amorphous polyolefin are preferable.

The form of the substrate A is, for example, a plate or a film. From theviewpoint of productivity and transportation, a plastic film ispreferable. In view of the transparency and productivity, thickness ofthe substrate A is preferably 10 to 500 μm, more preferably 50 to 200μm.

Next, the intermediate refractive index layer B is described. Since theintermediate refractive index layer B having a specific refractive indexand a specific optical thickness is formed between the substrate A andthe conductive layer C, the transparent conductive laminate film of thepresent embodiment has reduced reflection of purple light to blue light,whereby the coloring of the transmitted light is reduced.

The refractive index of the intermediate refractive index layer B is 1.7to 1.85, which is greater than the refractive index of the substrate Aand less than the refractive index of the conductive layer C. If therefractive index of the intermediate refractive index layer B is lessthan 1.7 or greater than 1.85, the degree of coloring of the transmittedlight increases.

The optical thickness of the intermediate refractive index layer B ispreferably in the range of 100 to 175 nm. By setting the opticalthickness of the intermediate refractive index layer B to apre-determined range, the reflectance of blue light (wavelength around400 nm) is particularly decreased. When the optical thickness is lessthan 100 nm or greater than 175 nm, the coloring of the transmittedlight becomes greater.

The material constituting the intermediate refractive index layer B isnot particularly limited as long as the refractive index does not exceedthe specific range and the object of the present embodiment is notimpaired, and a known material can be used. For example, an inorganicsubstance or a mixture of an inorganic substance and an organicsubstance can be used. Here, as the inorganic substance, for example,metal oxides such as zinc oxide, titanium oxide, cerium oxide, aluminumoxide, silane oxide, tantalum oxide, yttrium oxide, ytterbium oxide,zirconium oxide, indium tin oxide and antimony tin oxide can be used. Ofthese, zirconium oxide, titanium oxide, indium tin oxide, antimony tinoxide and cerium oxide are preferable, and zirconium oxide is mostpreferable from the viewpoint of the refractive index, electricalinsulating property and light resistance.

The method for forming the intermediate refractive index layer B is notparticularly limited, and for example, dry coating methods such as avapor deposition method, a sputtering method, an ion plating method, achemical vapor deposition (CVD) method and a plating method can beadopted. Of these, in view of the easiness of controlling the thicknessof the layer, the vapor deposition method and the sputtering method arepreferable.

When the intermediate refractive index layer B is made from a mixture ofan inorganic substance and an organic substance, for example, when theinorganic substance is fine particles of the aforementioned metal oxideand the organic substance is a curable monomer, the refractive index ofthe intermediate refractive index layer B can be easily adjusted and theintermediate refractive index layer B can be easily prepared. It ispreferable that the average particle size of the fine particles of themetal oxide does not exceed the thickness of the intermediate refractiveindex layer B by far. Specifically, the average particle size of thefine particles of the metal oxide is preferably not more than 0.1 μm,more preferably not more than 0.05 μm, and most preferably 0.01 to 0.05μm. A greater average particle size causes scattering and reduction ofthe transparency of the intermediate refractive index layer B, andtherefore is not preferable.

If necessary, the surface of the fine particles can be modified by acoupling agent. As coupling agents, for example, a silicon compound, ametal alkoxide obtained by substitution with an organic group in acompound containing a metal such as aluminum, titanium, zirconium andantimony and an organic acid salt can be used.

The curable monomer is not particularly limited and known one can beused. For example, a mono-functional or multi-functional (meth)acrylicacid ester, a silicon compound such as tetraethoxysilane can be used.The curable monomer is preferably an ultraviolet curable monomer in viewof the productivity and layer strength of the intermediate refractiveindex layer B, and a multi-functional monomer is preferably used in viewof the improvement of the layer strength. For these reasons, ultravioletcurable, multi-functional acrylates and silicon compounds are mostpreferable.

As the ultraviolet curable, multi-functional acrylate, for example,multi-functional alcohol derivatives such as dipentaerythritolhexaacrylate, tetramethylolmethane tetraacrylate, tetramethylolmethanetriacrylate, pentaerythritol pentaacrylate, trimethylolpropanetriacrylate, 1,6-hexanediol diacrylate,1,6-bis(3-acryloyloxy-2-hydroxypropyloxy)hexane and urethane acrylatessuch as polyethylene glycol diacrylate, pentaerythritol triacrylate andhexamethylene diisocyanate urethane prepolymer can be used. As thecurable monomer, a mixture of one or more kinds of the aforementionedmonomers or those to which another component is added can be used.

The mixing ratio of the fine particles of the metal oxide and thecurable monomer (the weight ratio of fine particles of metaloxide/curable monomer) is preferably 50/50 to 90/10, more preferably60/40 to 85/15. When the ratio of the fine particles of the metal oxideis less than 50 parts by weight, i.e., the ratio of the curable monomeris more than 50 parts by weight, an intermediate refractive index layerB having a desired refractive index cannot be obtained. When the ratioof the fine particles of the metal oxide is more than 90 parts byweight, i.e., the ratio of the curable monomer is less than 10 parts byweight, the molding property and strength of the intermediate refractiveindex layer B tend to decrease.

In the range that the effect of the present embodiment is not impaired,additives such as an inorganic or organic pigment, a polymer, apolymerization initiator, a polymerization inhibitor, an antioxidant, adispersant, a surfactant, a light stabilizer, a light absorbing agentand a leveling agent may be added to the material of the intermediaterefractive index layer B.

When the drying step is conducted after forming a layer according to awet coating method, an optional amount of solvent may be added to thematerial of the intermediate refractive index layer B. When the materialof the intermediate refractive index layer B is a mixture of aninorganic substance and an organic substance, the intermediaterefractive index layer B is usually formed by a wet coating method. Asthe wet coating method, a roll coating method, a spin coating method anda dip coating method are known. Preferable wet coating methods are theroll coating method and the dip coating method which enable continuouslayer forming and are high in productivity.

A conductive circuit of the transparent conductive laminate film isformed on the conductive layer C. The material of the conductive layer Cis not particularly limited, but a metal or a metal oxide is preferablyused. For example, a transparent conductive layer containing a metalsuch as gold, silver, copper, platinum and nickel or a metal oxide suchas tin oxide, indium tin oxide (ITO) and antimony tin oxide ispreferable. Of these, indium tin oxide (ITO) is more preferable from theviewpoint of conductivity, transparency and stability.

The method for forming the conductive layer C is not particularlylimited, and for example, a dry coating method such as a vapordeposition method, a sputtering method, an ion plating method, a CVDmethod and a plating method can be adopted. Of these, from the viewpointof controlling the thickness of the layer, the vapor deposition methodand the sputtering method are particularly preferable.

The layer thickness of the conductive layer C is in the range of 10 to60 nm in terms of the optical thickness. When the optical thickness isless than 10 nm, the surface resistance becomes high. On the other hand,when the optical thickness is more than 60 nm, the transparencydecreases.

A hard coat layer, for example, may be formed between the substrate Aand the intermediate refractive index layer B to improve hardness. Foranti-dazzling, preventing a Newton ring from occurring, improvingadhesion between the layers and blocking light having a specificwavelength, at least one functional layer may be formed. As the materialof the functional layer, inorganic substances such as silicon oxide,organic substances such as ultraviolet-curable and multi-functionalacrylate or a mixture thereof may be used. The thickness of thefunctional layer is preferably 0.005 to 20 μm, and the refractive indexis preferably in the range of 1.45 to 1.65. The method of forming thefunctional layer is not particularly limited, and known methods such asdry coating methods and wet coating methods can be used.

As long as the effect of the present embodiment is not impaired,additives such as an inorganic filler, an inorganic or organic pigment,a polymer, a polymerization initiator, a polymerization inhibitor, anantioxidant, a dispersant, a surfactant, a light stabilizer, a lightabsorbing agent and a leveling agent may be added to the material of thefunctional layer. When the drying step is conducted after forming alayer according to a wet coating method, an optional amount of solventmay be added to the material of the functional layer.

By adjusting the refractive index and the optical thickness of eachlayer so that the reflectance curve of the surface closer to theconductive layer in the transparent conductive laminate film has a localminimal value in the wavelength range of 380 to 500 nm, reflection ofpurple to blue light can be further reduced and the coloring of thetransmitted light can be further reduced.

In the following, the wavelength at which the reflectance exhibits thelocal minimal value is referred to as a local minimum reflectancewavelength. When the local minimum reflectance wavelength is shorterthan 380 nm or longer than 500 nm, the transmitted light tends to becolored because the effect of reducing the reflection of purple to bluelight is low or because the reflection becomes greater.

By adjusting the refractive index and the optical thickness of eachlayer so that the local minimum reflectance wavelength on the surfacecloser to the aforementioned conductive layer is in the range of 380 to500 nm, the color difference of the transmitted light indicated byL*a*b* color system in accordance with JIS Z8729 falls into the range of−2<a*<2, −2<b*<2. Accordingly, a transparent conductive laminate filmsubstantially free of the problem of coloring can be produced.

When the refractive index and the optical thickness are adjusted so thatthe local minimum reflectance wavelength is in the range of 450 to 500nm, the reflection of purple to blue light can be further decreased. Asa result, the coloring of the transmitted light is further decreased,and it is more preferable because the total transmittance of thetransparent conductive laminate film in accordance with JIS K7361-1becomes not less than 85%.

The transparent conductive laminate film can be used for purposes whichrequire a high light transmittance and superior color tone as aconductive material. In particular, it can be used for electronic imagedisplay devices such as an organic or inorganic electro luminescencedisplay and a liquid crystal display or for electrode substrates ofresistive touch panels.

If necessary, an adhesion layer can be formed in advance on the surfaceof the transparent conductive laminate film where the conductive layeris not formed and the laminate film can be used by adhering to theobject. The material to be used for the adhesion layer is notparticularly limited, and examples thereof include a silicone adhesive,an acrylic adhesive, an ultraviolet curable adhesive and a thermosettingadhesive.

When the laminate film is used as an upper (contact surface side)electrode substrate in a resistive touch panel, a hard coat layer ispreferably formed on the surface of the transparent conductive laminatefilm opposite to the conductive layer C for improving the surfacestrength. At least one kind of property such as anti-dazzling property,antistatic property and reduced reflection can be imparted to the hardcoat layer. The surface of the transparent conductive laminate filmopposite to the conductive layer C can be closely laminated to thebackside of the substrate having a hard coat layer via an adhesivelayer.

When used as an lower (display device side) electrode substrate of aresistive touch panel, the transparent conductive laminate film can beused as it is or by laminating with a substrate such as glass orplastic. In addition, on the backside, an anti-reflection layerincluding at least one layer can be formed directly or indirectly viaone or more layers, or a substrate having an anti-reflection layer canbe laminated to improve the light transmittance. The anti-reflectionlayer is not particularly limited and known materials can be used.

The transparent conductive laminate film of the present embodiment iscomposed of an intermediate refractive index layer B having an opticalthickness of 100 to 175 nm on a substrate A and a conductive layer Chaving an optical thickness of 10 to 60 nm laminated thereon. That is,the transparent conductive laminate film is made by forming only anintermediate refractive index layer B between the substrate A and theconductive layer C. Therefore, the structure is simpler than themulti-layer structure and the film can be prepared easily.

The refractive index of the intermediate refractive index layer B is 1.7to 1.85 and greater than the refractive index of substrate A and lessthan the refractive index of the conductive layer C. Accordingly, asshown in FIG. 3, the reflectance of the light incident upon thetransparent conductive laminate film is decreased and nearly fixed inthe wavelength range of 400 to 780 nm, and the coloring of thetransmitted light is inhibited. Further, as shown in FIG. 4, thetransmittance (total transmittance) is nearly fixed at 85% and thetransmitted light is bright. As mentioned above, because the refractiveindex of the intermediate refractive index layer B is adjusted to avalue between the refractive index of the substrate A and the refractiveindex of the conductive layer C, the characteristic curve of thereflectance of the transparent conductive laminate film relative towavelength is relatively flat (the difference between the local maximalvalue and the local minimal value of the reflectance is relativelysmall). Therefore, the coloring of the transmitted light can beprevented. In addition, the transmittance is high regardless of thewavelength and nearly fixed, and therefore the transmitted light can bemade bright.

The following advantages are obtained by the preferred embodiment.

In the transparent conductive laminate film, a substrate A, anintermediate refractive index layer B and a conductive layer C arelaminated in that order, directly or indirectly via at least one layer.The optical thickness of the intermediate refractive index layer B is100 to 175 nm, and the optical thickness of the conductive layer C is 10to 60 nm. The refractive index of the intermediate refractive indexlayer B is 1.7 to 1.85, which is between the refractive index of thesubstrate A and the refractive index of the conductive layer C.Accordingly, the coloring of the transmitted light can be reduced. Inaddition, since the number of layers constituting the laminate film issmall, the transparent conductive laminate film has a simpleconstitution and can be produced easily at a low cost. Accordingly, thetransparent conductive laminate film of the present embodiment is usefulas an electrode substrate for touch panels.

Since the conductive layer C is formed by a metal or a metal oxide, anexcellent surface resistance can be obtained.

The conductive layer C can be easily formed by a method selected from avacuum deposition method, an ion plating method, a CVD method and asputtering method using indium tin oxide.

Since the substrate A is a plastic film having a thickness of 10 to 500μm, the transparent conductive laminate film can exhibit stabletransparency.

Since the intermediate refractive index layer B is formed by a wetcoating method using raw materials, film forming can be conducted withease and the cost for producing a transparent conductive laminate filmcan be reduced.

In the transparent conductive laminate film, the local minimumreflectance wavelength on the surface closer to the conductive layer Cis in the range of 380 to 500 nm. Accordingly, the blue reflection lightin the reflection spectrum can be reduced and coloring to yellow can bereduced.

In the transparent conductive laminate film, the local minimumreflectance wavelength on the surface closer to the conductive layer Cis in the range of 450 to 500 nm. Accordingly, coloring to yellow can bereduced without decreasing the total transmittance.

Since the color difference of the transmitted light indicated by theL*a*b* color system in accordance with JIS Z8729 is −2<a*<2 and −2<b*<2,and close to zero, the coloring of the transparent conductive laminatefilm can be prevented.

EXAMPLES

Examples of the present invention will now be explained in more detail.The present invention is not limited to the following Examples. Therefractive indexes of the layers other than the conductive layer weremeasured according to the following procedure.

(1) Coating solutions for each layer were coated on a PET film having arefractive index of 1.63 (product name: A4100, available from ToyoboCo., Ltd.) using a dip coater (made by SUGIYAMA-GEN RIKAGAKUKIKI CO.,LTD.), while adjusting the optical thickness (n×d) to about 110 nm afterdrying.

(2) The coated layer was dried and then hardened by irradiation ofultraviolet ray (ultraviolet irradiation apparatus: 120W high pressuremercury lamp, 400 mJ, made by IWASAKI ELECTRIC Co., Ltd.,) undernitrogen atmosphere.

(3) The backside of the PET film (the side opposite to the cured layer)was roughened by polishing using sandpaper and coated over with a blackcoating to prepare a test piece. The specular reflection spectrum (380to 780 nm, +5°, −5°) of the test piece was measured using aspectrophotometer (product name “U-best 50”, made by JASCO Corporation).

(4) The refractive index was calculated using the local maximal value orthe local minimal value of the reflectance obtained from the reflectionspectrum, based on the following formula.

$\begin{matrix}{{{Local}\mspace{14mu}{minimal}\mspace{14mu}{value}\mspace{14mu}{of}\mspace{14mu}{{reflectance}(\%)}} = {\left\{ \frac{n_{M} - n^{2}}{n_{M} + n^{2}} \right\}^{2} \times 100}} & (1)\end{matrix}$where n_(M) represents the refractive index of the PET film and nrepresents the refractive index of the layer.

As for the refractive index of the conductive layer, a conductive layerwas formed on a PET film having a refractive index of 1.63 (productname: A4100, available from Toyobo Co., Ltd.), so that the opticalthickness (n×d) became about 110 nm, and the refractive index wasmeasured according to the aforementioned procedures (3) and (4).

Preparation Example 1 Preparation of Coating Solution for IntermediateRefractive Index Layer (H-1)

A coating solution for intermediate refractive index layer (H-1) wasprepared by mixing 80 parts by weight of fine particles of zirconiumoxide (average particle size: 0.04 μm), 15 parts by weight oftetramethylolmethane triacrylate, 900 parts by weight of butyl alcohol,and 1 part by weight of a photopolymerization initiator (product nameIRGACURE 907 available from Ciba-Geigy Ltd). The refractive index of thecured product obtained by ultraviolet curing of the coating solution H-1was 1.77.

Preparation Example 2 Preparation of Coating Solution for IntermediateRefractive Index Layer H-2

Eighty parts by weight of fine particles of titanium oxide (averageparticle size: 0.03 μm) was used instead of 80 parts by weight of thefine particles of zirconium oxide (average particle size: 0.04 μm).Except for that, coating solution for intermediate refractive indexlayer H-2 was prepared in the same manner as in Preparation Example 1.The refractive index of the cured product obtained by ultraviolet curingof the coating solution H-2 was 1.85.

Preparation Example 3 Preparation of Coating Solution for Hard CoatLayer (HC-1)

A coating solution for hard coat layer HC-1 was prepared by mixing 70parts by weight of dipentaerythritol hexaacrylate, 30 parts by weight of1,6-diacryloyloxy hexane, 4 parts by weight of photopolymerizationinitiator (product name: IRGACURE 184 available from Ciba-Geigy Ltd.)and 100 parts by weight of isopropyl alcohol. The refractive index ofthe cured product obtained by ultraviolet curing of the coating solutionHC-1 was 1.52.

Preparation Example 4 Preparation of Hard-Coat Treated PET Film

The coating solution HC-1 prepared in Preparation Example 3 was coatedon a PET film having a thickness of 188 μm (product name: A4100,available from Toyobo Co., Ltd., refractive index 1.63) using a barcoater so that the layer thickness after drying became about 5 μm toform a coating solution layer. The coating solution layer was cured byirradiation of ultraviolet ray (ultraviolet irradiation apparatus: 120Whigh pressure mercury lamp, 400 mJ, made by IWASAKI ELECTRIC Co., Ltd.,)to prepare a hard-coat treated PET film.

Preparation Example 5 Preparation of dispersion of silica fine particles(L-1)

A dispersion of silica fine particles (L-1) was prepared by mixing 25parts by weight of tetramethylolmethane triacrylate, 220 parts by weightof dispersion of silica fine particles (product name: XBA-ST, availablefrom NISSAN CHEMICAL INDUSTRIES, LTD.), 900 parts by weight of butylalcohol and 5 parts by weight of photopolymerization initiator (productname: KAYACURE BMS, available from NIPPON KAYAKU CO., LTD.). Therefractive index of the cured product obtained by ultraviolet curing ofthe dispersion L-1 was 1.50.

Example 1

An intermediate refractive index layer B was formed on a PET film havinga thickness of 188 μm (product name: A4100, available from Toyobo Co.,Ltd., refractive index 1.63) using the coating solution for intermediaterefractive index layer H-1 according to the following method.

A coating solution layer was formed by applying the coating solution forintermediate refractive index layer H-1 in an amount that the opticalthickness after curing became 160 nm using a dip coater (made bySUGIYAMA-GEN RIKAGAKUKIKI CO., LTD.). The coating solution layer wasdried and cured by irradiation of ultraviolet ray (ultravioletirradiation apparatus: 120W high pressure mercury lamp, 400 mJ, made byIWASAKI ELECTRIC Co., Ltd.,) under nitrogen atmosphere to form anintermediate refractive index layer B.

The film having an intermediate refractive index layer B was subjectedto pre-drying at 100° C. for an hour. By sputtering using an ITO(indium:tin=92:8 refractive index after forming layer 2.00) target, aconductive layer C having an optical thickness of 40 nm was formed onthe intermediate refractive index layer B. The transparent conductivelaminate film 100 of FIG. 1 was prepared.

The transparent conductive laminate film 100 has a substrate A includingPET film, an intermediate refractive index layer B formed on thesubstrate A and a conductive layer C formed on the layer B.

Then, the total transmittance, the local minimum reflectance wavelength,the color difference of the transmitted light (a*, b*) and the surfaceresistance of film 100 were measured according to the following method.The results are shown in Table 1.

(1) The total transmittance was measured by using a haze meter (productname: NDH2000, made by Nippon Denshoku Industries Co., Ltd.).

(2) The local minimum reflectance wavelength was obtained from thereflection spectrum measured at 380 to 780 nm by using aspectrophotometer (product name: UV1600, made by Shimadzu Corporation).

(3) The transmitted color difference (a*, b*) was measured by using acolor-difference meter (product name: SQ-2000, made by Nippon DenshokuIndustries Co., Ltd.).

(4) The surface resistance was measured by using a surface resistivitymeter (product name: Loresta MP MCP-T350, made by Mitsubishi ChemicalCorporation).

TABLE 1 Examples Comparative Examples 1 2 3 4 1 2 3 4 5 6 refractiveindex of 1.77 1.77 1.77 1.85 — 1.77 1.77 1.50 2.30 — intermediate layeroptical thickness of 160 120 160 160 — 90 190 160 160 — intermediatelayer (nm) Hard Coat Layer none none formed formed none none none nonenone none total transmittance (%) 86.1 82.2 87.5 87.8 86.2 81.2 88.187.1 75.1 88.9 local minimal 480 400 500 500 — 350 530 — 430 550reflectance wavelength (nm) color difference a* −1.1 0.7 −1.3 −1.6 −0.30.8 −2.4 −0.1 −0.1 −3.9 of transmitted b* 0.5 −0.8 0.3 0.2 3.0 2.2 4.65.1 −8.2 5.9 light surface resistance (Ω) 3 × 10² 3 × 10² 3 × 10² 3 ×10² 3 × 10² 3 × 10² 3 × 10² 3 × 10² 3 × 10² 3 × 10²

Example 2

A transparent conductive laminate film was prepared in the same manneras in Example 1 except that the optical thickness after curing waschanged to 120 nm.

Example 3

A transparent conductive laminate film was prepared in the same manneras in Example 1 except that the hard-coat treated PET film prepared inPreparation Example 4 was used instead of the PET film.

Example 4

A transparent conductive film was prepared in the same manner as inExample 3 except that the refractive index of the intermediate layer waschanged to 1.85.

Comparative Example 1

A transparent conductive laminate film was prepared by forming aconductive layer C directly on a PET film having a thickness of 188 μm(product name: A4100, available from Toyobo Co., Ltd., refractive index1.63), in the same manner as in Example 1.

Comparative Example 2

A transparent conductive laminate film was prepared in the same manneras in Example 1 except that the optical thickness after curing waschanged to 90 nm.

Comparative Example 3

A transparent conductive laminate film was prepared in the same manneras in Example 1 except that the optical thickness after curing waschanged to 190 nm.

Comparative Example 4

A transparent conductive film was prepared in the same manner as inExample 1 except that the optical thickness after curing was changed to160 nm and the dispersion of silica fine particles (L-1) (refractiveindex: 1.50) was used instead of the coating solution for intermediaterefractive index layer H-1.

Comparative Example 5

A metal oxide layer (refractive index: 2.30, optical thickness: 160 nm)was formed on a PET film having a thickness of 188 μm (product name:A4100, available from Toyobo Co., Ltd., refractive index: 1.63) as anintermediate refractive index layer by sputtering using a titanium oxidetarget. A transparent conductive laminate film was prepared by forming aconductive layer (optical thickness: 40 nm) on the metal oxide layer bysputtering using an ITO (indium:tin=92:8) target.

Comparative Example 6

A transparent dielectric film having a thickness of 100 nm and arefractive index of 2.35 was formed on one surface of a PET film byvacuum deposition of titanium oxide according to electron beam heatingunder a reduced pressure of 1 to 2×10⁻⁴ Torr (1.33 to 2.66×10⁻² Pa).Then, a conductive layer C was formed in the same manner as in Example 1to prepare a transparent conductive laminate film.

As shown in Table 1, the transparent conductive films of Example 1 to 4had a low surface resistance and were highly conductive. In addition,the small transmitted color difference (a*,b*) reveals that the coloringwas little.

On the other hand, in Comparative Examples 1 and 6 which have nointermediate refractive index layer B and in Comparative Examples 2 and3 in which the optical thickness of the intermediate refractive indexlayer B is outside the pre-determined range and in Comparative Example 4in which the refractive index of the intermediate refractive index layeris less than the pre-determined range, it was shown that the transmittedcolor difference, in particular, the value of b* became greater, causingthe coloring of the transmitted light.

In Comparative Example 5 in which the refractive index of theintermediate refractive index layer is higher than the refractive indexof the conductive layer, it was shown that the transmitted colordifference, in particular, the value of b* became extremely small,causing the coloring of the transmitted light.

Examples 5 and 6

The backside of the hard-coat treated PET film prepared in PreparationExample 4 was evenly laminated on the backside of the transparentconductive laminate films of Examples 3 and 4 via acrylic adhesive sheet(product name: NONCARRIER, available from Lintec Corporation). Aconductive layer of ITO (indium:tin =92:8) was formed on a glass platehaving a thickness of 2 mm (product name: FL 2.0, available from NipponSheet Glass Co., Ltd.) by a sputtering method as in Example 1. Next, theconductive layer of the transparent conductive laminate film and theconductive layer of the glass plate were faced with each other and theall sides were adhered by double-stick tape to prepare a resistive touchpanel 200 shown in FIG. 2.

The resistive touch panel 200 includes a transparent conductive laminatefilm 100 a in which an intermediate refractive index layer B and aconductive layer C are laminated via the first hard coat layer 1 formedon the substrate A. The transparent conductive laminate film 100 a isbonded to a PET film 3 having the second hard coat layer 2 via anadhesive layer 4. The touch panel 200 includes a conductor layer 6formed on a glass substrate 5. This conductor layer 6 is bonded to theconductive layer C of the transparent conductive laminate film 100 a viadouble-stick tape 7.

The total transmittance and transmitted color difference (a*,b*) of theresistive touch panel 200 were measured in the same manner as inExample 1. The results are shown in Table 2.

Comparative Examples 7 to 9

A resistive touch panel was prepared in the same manner as in Example 5except for using as a transparent conductive film the film ofComparative Example 1 in Comparative Example 7, the film of ComparativeExample 2 in Comparative Example 8 and the film of Comparative Example 3in Comparative Example 9, respectively. The total transmittance andtransmitted color difference (a*,b*) of the resistive touch panels wereas shown in Table 2.

As shown in Table 2, the touch panels of Examples 5 and 6 had a lowtransmitted color difference and the coloring of the transmitted lightwas not noticeable.

On the other hand, the touch panel of Comparative Example 7 using a filmwhich does not have an intermediate refractive index layer B and thetouch panels of Comparative Examples 8 and 9 using a film in which theoptical thickness of the intermediate refractive index layer is notadequate had a large transmitted color difference, in particular, anextremely large b* value, and the transmitted light colored yellow.

TABLE 2 Examples Comparative Examples 5 6 7 8 9 refractive index of 1.771.85 — 1.77 1.77 intermediate layer optical thickness of 160 160 — 90190 intermediate layer (nm) Hard Coat Layer formed formed none none nonetotal transmittance (%) 80.3 80.4 79.1 74.6 81.1 color difference a*−1.5 −1.8 −0.5 0.1 −1.7 of transmitted b* 1.5 1.7 4.3 3.4 6.0 light

The obtained touch panels were installed in a CRT display and tested thefunctions. The touch panels of Examples 5 and 6 were capable ofindicating all colors on the CRT display accurately, but in the touchpanels of Comparative Examples 7 to 9, white on the CRT display wasyellowish.

The preferred embodiment can be modified as follows.

The intermediate refractive index layer B may be composed of two layers.Of the two intermediate refractive index layers B, it is preferable thatthe layer closer to the substrate A has a small refractive index and thelayer closer to the conductive layer C has a greater refractive index,in the refractive index range of 1.7 to 1.85. In this case, thereflectance of the transparent conductive laminate film can be madesmaller and the transmittance higher.

The optical thickness and the refractive index of the intermediaterefractive index layer B may be determined according to the followingformula so that the reflected light from the surface of the substrate Ainterferes with the reflected light from the surface of the intermediaterefractive index layer B to cancel each other out. In the formula, λrepresents the wavelength of the reflected light.2×(optical thickness of intermediate refractive index layer B)/λ=½

Electron beam may be irradiated when the intermediate refractive indexlayer B is formed by curing a mixture of metal oxide and curablemonomers by a wet coating method. In this case, the intermediaterefractive index layer B cures rapidly.

The viscosity may be adjusted to achieve a desired optical thickness byadding a viscosity controlling agent (thickener) to the mixed solutionof metal oxide and curable monomers for forming an intermediaterefractive index layer B.

1. A transparent conductive laminate film comprising: a lighttransmitting substrate; an intermediate layer laminated on one or bothsurfaces of the substrate directly or indirectly via at least one layerand having an optical thickness of 100 to 175 nm; and a conductive layerlaminated on the intermediate layer and having an optical thickness of10 to 60 nm, wherein the intermediate layer has a refractive index of1.7 to 1.85, and wherein the refractive index of the light transmittingsubstrate is less than the refractive index of the intermediate layer,and the refractive index of conductive layer is greater than therefractive index of the intermediate layer (refractive index ofsubstrate<refractive index of intermediate layer<refractive index ofconductive layer).
 2. The transparent conductive laminate film accordingto claim 1, wherein the conductive layer is made of a metal or a metaloxide.
 3. The transparent conductive laminate film according to claim 1,wherein the conductive layer contains indium tin oxide.
 4. Thetransparent conductive laminate film according to claim 1, wherein thesubstrate is a plastic film having a thickness of 10 to 500 nm.
 5. Thetransparent conductive laminate film according to claim 1, which has afirst surface located closer to the conductive layer, wherein the firstsurface has a local minimum reflectance wavelength within the range of380 to 500 nm.
 6. The transparent conductive laminate film according toclaim 5, wherein the first surface has a local minimum reflectancewavelength within the range of 450 to 500 nm.
 7. The transparentconductive laminate film according to claim 1, which has a transmittedcolor difference of −2<a*<2 and −2<b*<2 in a L*a*b color system.
 8. Thetransparent conductive laminate film according to claim 1, wherein theconductive layer is in contact with the intermediate layer and thesubstrate.
 9. The transparent conductive laminate film according toclaim 1, wherein the intermediate layer is a mixture of an inorganicsubstance and an organic substance.
 10. The transparent conductivelaminate film according to claim 9, wherein the intermediate layer is acured product of a mixture of a metal oxide and a curable monomer. 11.The transparent conductive laminate film according to claim 10, whereinthe curable monomer is an ultraviolet-curable monomer.
 12. A touch panelcomprising: electrode substrates faced with each other; and atransparent conductive laminate film laminated above the electrodesubstrates, wherein the transparent conductive laminate film includes alight transmitting substrate, an intermediate layer laminated on one orboth surfaces of the substrate directly or indirectly via at least onelayer and having an optical thickness of 100 to 175 nm, and a conductivelayer laminated on the intermediate layer and having an opticalthickness of 10 to 60 nm, wherein the intermediate layer has arefractive index of 1.7 to 1.85, and wherein the refractive index of thelight transmitting substrate is less than the refractive index of theintermediate layer, and the refractive index of the conductive layer isgreater than the refractive index of the intermediate layer (refractiveindex of substrate<refractive index of intermediate layer<refractiveindex of conductive layer).